2017 programme The Filtration Society programme for 2017

Testing is a critical feature of quality control during filter element manufacture and integrity validation during filter operation. Equally important in filter applications is a good understanding of the feed to be filtered and the filter medium itself, which require characterisation in many different ways.

This two day event will bring together people interested in characterisation, testing and filter media technologies that are being applied in industry, as well as those that are about to become industrially accepted methods. From tightening legislation to the growing number of finer, more demanding, filter processes, new filter media developments are constantly being driven by customer requirements. This, and newer regulatory frameworks and standards, require ever better test methodologies.

Many new developments have taken place in recent years in both gas and liquid applications. Theconference will feature key elements of these developments, and will be of particular interest to process engineers, designers, technical and R&D staff, research institutes and decision makers.

An exhibition of equipment will complement the conference, where some of the latest technologies in the market place will be demonstrated by manufacturers and suppliers.

Volume 17, Issue 2 Abstracts from the FILTRATION journal

The ‘maximum’ pore size in a sand screen, when challenged by glass microspheres, can be defined as the 97th percentile (the Cut Point), the 99th percentile or the single largest sphere passing the mesh. When analysing the microspheres by Image Analysis, this paper shows that, provided at least 1000 spherical beads (maximum size/minimum size <1.2) are analysed, the measurement uncertainty is approximately 3% for both d97 and d99. However, the uncertainty for the Maximum Penetrating Particle (MPP) went up to 17% and so cannot be recommended as a reliable parameter. Excellent agreement was found between the Ultrasonic wet test method and the Sonic dry test method.

Pre-calibrated, narrow size distribution glass microspheres were used to investigate the most appropriate measure of the ‘maximum’ pore sizes of sand screens. Using a calibration graph of weight passing versus cut point, the measurement uncertainty in a dry challenge test was only 3-4% (this compared with the inherent measurement uncertainty of 1% when the same mesh was analysed 10 times). Analysis of the beads passing three different sand screens by microscopy and image analysis confirmed that the cut point corresponded to the D97 and the measurement uncertainty remained at 3-4% up to D99, herein defined as the ‘maximum’ pore size. The uncertainty for the single largest sphere passing the mesh (D100) was too high (+/-15%) to be of any practical value and could cause confusion in the industry.

The cake properties presented as specific cake resistance and cake porosity provide essential information about the flux decline behaviour in deadend membrane filtration such as microfiltration and ultrafiltration controlled by the cake filtration mechanism. Initially, various types of constitutive equations are shown to represent local specific cake resistance and local cake porosity as functions of the solid compressive pressure. It is also shown that their average values can be analytically derived from such local values based upon the compressible cake filtration theory and vice versa.

In the filtration testing methods, the pressure dependence of the average specific cake resistance was available over wide ranges of pressure drop across the filter cake by carrying out a single constant pressure deadend filtration using a membrane with an extremely high flow resistance. Step-up pressure filtration using a filtration cell with a single stage reduction in the effective filtration area allowed us to obtain the pressure dependence not only of the average specific cake resistance but also of the average cake porosity from only one run by making use of the decrease in the cake thickness caused by the cake compression arising from stepped-pressure operation. In sedimentation testing methods such as analytical ultracentrifugation, permeability data were evaluated by measuring sedimentation velocities at various solid concentrations, and the compression data were estimated by measuring the thicknesses of sediments obtained under various rotor speeds of the test cell. These data successfully described the flux decline behaviour observed in the deadend ultrafiltration of nanocolloids.

Volume 17, Issue 1 Abstracts from the FILTRATION journal

The design and characteristics of filter media, such as weave pattern, number of pores, pore shape, pore size, pore size distribution and permeability influence cake formation, cake filtration, particle retention, filter media lifetime as well as the resulting machine efficiency and productivity. In the end, the overall cost of ownership is affected.
By carrying out intensive laboratory analysis, filtration trials and scale-up testing, the influence of filter media design on the final filtration result during vacuum and pressure filtration is investigated and described in this paper. If everything is calculated and implemented thoroughly there can be a substantial contribution to achieving a higher production yield, while obtaining, or even improving, the final product quality. The paper compares the variables and performance criteria that require definition in order to select the most efficient filter media for a given application. An actual example of the guidelines used to judge filter media performance and some of the properties of enhanced future filter media is presented to conclude the paper.

Scalable Double Layer Weave (DLW) filter fabrics for different applications and requirements are presented. Laboratory and field tests illustrate how filtration results are dependent on the selection of appropriate filter media and their specific properties. Improved cake dryness and purity, better cake release, higher production capacity and, in the end, lower process costs result from new filter media design and careful selection.

As industry strives for increased levels of efficiency through rigorous process optimisation programmes, filter media suppliers must seek to add value to their products by improving product performance, lifetime, ease-of-use and maximising process up-time. Clear Edge has developed a comprehensive body of practical knowledge in solid-liquid separation together with a strong scientific understanding, using its state-of-the-art laboratories to understand the chemical and structural properties required to maximise performance. By way of illustration, two innovative filter media technologies are described herein.

It has been demonstrated that microporous coated media can improve blinding resistance, enhance throughput and improve filtrate clarity; these properties are mainly attributed to the surface filtration mechanism afforded by the microporous coating which is impregnated both onto and into the base filter media. Additional productivity gains result from increased retention efficiencies. To further enhance the value proposition, this technology can be used in combination with the elastomeric welded barrel neck product line, Coreflo™, which affords ease of cloth fitting with a leak free seal. Combining innovative solutions such as these results in tangible benefits for the customer: to demonstrate this the findings from a number of case studies are presented to prove the measurable added value of these technologies, either alone or used in combination.

INSIGHT INTO THE STICKY PHASE OF ACTIVATED SLUDGE AND ITS
IMPLICATION TO SLUDGE DEWATERING/DRYING OPERATIONS
Bart Peeters and Luc Vernimmen (pages 57-60)

The sticky phase of wastewater sludge poses a persistent challenge when the sludge volume is reduced in industrial dewatering-drying installations. At some intermediate dryness content, during its passage through mechanical dewatering and consecutive thermal drying, the sludge transforms into a rubbery material. This either adheres to the equipment surfaces or further agglomerates into large lumps by cohesion, thereby impeding the proper working of these unit operations. Although insight in the sticky phase of sludge is essential for smooth operations in industry, most literature pertains to research conducted in the context of sludge dewatering and drying as such, rather than to the concomitantly appearing sticky behaviour.

In this paper, we discuss the sticky phase: how it can be mapped, how its existence can be explained and how industry copes with it during daily operations. One strategy to deal with the stickiness, rigorously tested by the authors at lab- and full-scale over the past six years, is the conditioning of the sludge with polyaluminium chloride (PACl) which will be specifically highlighted.

Volume 16, Issue 4 Abstracts from the FILTRATION journal

This paper describes some of the features of new equipment for laboratory scale filtration testing. Descriptions are provided for the Filtration Performance Test, which facilitates the automated acquisition of constant pressure filtration data, and Filtration Performance Software which facilitates data analysis, including the automated calculation of characterising parameters such as specific cake resistance and filter cake compressibility. Exemplar experimental data are presented to show equipment and analysis performance in relation to repeatability measurements, filtration cell diameter, particle diameter and particle shape. The use of the approach to aid process scale equipment specification is also considered and some examples are provided.

This paper presents two studies of how computational fluid dynamics (CFD) has been used by GKD to improve the performance of filter media and aid the determination of characterising parameters. In the first study CFD is used to help specify a more robust filter medium for an oil/gas application which consequently facilitated higher daily production rates. In the second study CFD is used as a numerical simulation of the well-known bubble point test and favourable comparisons are made with experimental measurements.

The properties, especially cake compressibility, of the filter cake formed in deadend ultrafiltration were examined using nanocolloids of bovine serum albumin (BSA) solutions at pH 5.1 (around the isoelectric point) and 7.0, and nanosilica sol. Although average porosity of the filter cake formed in the ultrafiltration of nanosilica sol varied significantly with the applied filtration pressure, the variation of average specific cake resistance with the applied pressure was not as pronounced when compared to results obtained with the BSA solutions.

The specific surface area of solid particles, evaluated from the relation between the local specific cake resistance and local cake porosity derived from the flux decline behaviour in deadend ultrafiltration with the aid of the Happel cell model, was examined. It was revealed that BSA molecules easily deformed compared to silica nanoparticles under the action of the solid compressive pressure generated from the filtrate flow in ultrafiltration. Moreover, it was found that BSA molecules at pH 5.1, the isoelectric point, deformed more significantly than those at pH 7.0 due to the compression force. This was also backed up from the relation between the specific surface area and solids compressive pressure over a relatively low solids compressive pressure range obtained by measuring the sedimentation velocity and equilibrium thickness of the compressed sediment in analytical ultracentrifugation of BSA solutions.

Volume 16, Issue 3 Abstracts from the FILTRATION journal

NEW FILTRATION PLANT FOR THE STORAGE OF BAUXITE RESIDUES AT AN ALUMINA REFINERY
Lloyd Holliday, R. Medeiros, M. de Castro and V. Hartmann (pages 158-164)

Hydro Alunorte have historically used vacuum drum filters for red mud filtration and Giulini dry stacking technology for residue storage. Studies have been completed and Hydro is now implementing new technology with a new filtration plant that uses fast opening filter presses and a change to dry residue storage. The new system, which is under construction, will increase the solids content of the residues to 78% w/w solids, decrease the caustic content in the residues, increase the recovery of caustic soda for reuse, reduce the ratio of washing water to red mud solids, significantly decrease the land area needed for residue disposal and lower the amount of surface water to be treated. The new technology is considered to be the most sustainable way forward for the industry.

Instead of using an independent engineering company, Hydro decided to draw on the expertise and experience of the filtration equipment supplier for the design and construction of the filtration plant. This paper gives an overview of the most important considerations when designing a filter press plant for red mud. Most important is personnel health and safety in operation and maintenance because the process is abrasive, corrosive, scaling and at high temperature. To achieve high plant availability the filter presses are designed to have less and larger components. The logistics within the plant for the storage and changing of filter cloths for the largest filter plates in the world (2.5 m x 3.5 m) will be important. Plant performance is to be controlled by process optimisers.

PRODUCED WATER TREATMENT: PILOT TEST RESULTS OF AN INTEGRATED MECHANICAL AND MEMBRANE SYSTEM
Arian Edalat and Eric Hoek (pages 164-167)

This paper describes an integrated technology for the treatment of produced water. The results of two field trials are presented in order to demonstrate equipment performance.

The aim of this study was to improve understanding of sustainability for a ‘minimum impact’ copper concentrator during an estimated 15 years long mine lifetime; background information from earlier studies of minimum impact Cu concentrator operational risk results were used. The operational risks focused on decreasing water stress, environmental hazards, and possible dam break-up. In this paper, the main focus has been set on a conceptual study of simulation and calculation of economics for four different tailings management facility methods and their impact on the site water balance as well as the sustainability assessment.

The selected tailings treatment flowsheets considered in the study are:

All mass balance calculations where performed using Outotec’s HSC Chemistry simulation tool, that provided the basis for the cost calculation. The costs were estimated based on a Finnish cost basis with an assurance of ±30%. The selected location for the concentrator was a flat mine site in a temperate climate zone. Such a scenario showed that the filtered option decreases the water footprint significantly, i.e. from 26.7 to 5.8 kg blue water/kg concentrate produced (or 0.51 to 0.11 kg blue water/kg ore feed) as well as improving the water quality and toxicity indicators.

The simulation results were also used to perform an environmental assessment using the GaBi software. There was no significant carbon footprint and acidification potential variation between the four cases 0.55-0.58 kg CO2-eq/ca. kg blue water/kg concentrate or ca. 0.011 kg CO2-eq/ca. kg blue water/kg ore (when rounded).

There are several important parameters required to unambiguously define pore size in a filter by the challenge test method:

(a) How the pore shape is to be defined
(b) The shape of the challenge particles used
(c) The definition of ‘maximum’ pore
(d) The uncertainty of the measurement.

In addition, the particle sizing instrument used in the analysis must a ‘primary’ method. That is, the results must be traceable back to the International Metre, without any ‘black box’ manipulation.

This paper uses a wide range of woven wire mesh filters from several hundred microns down to a few microns in conjunction with precision glass microspheres to unambiguously characterise the filters. Aqueous suspensions of the filter standards were used as the transport mechanism through the meshes and the penetrating spheres measured by microscopy and image analysis. Provided at least 1000 spherical beads (Maximum size/minimum size <1.2) were analysed, the measurement uncertainty was approximately 3% for both d97 and d99. However, the uncertainty for the d100, Maximum Penetrating Particle (MPP), went up to over 20% and so cannot be recommended as a reliable parameter.

Volume 16, Issue 2 Abstracts from the FILTRATION journal

This paper provides a description of an alternative (disc filter) technology to conventional sand filters. A new Plain Dutch Weave mesh called ODW 6 is discussed, and some performance indicators are presented.

This research utilises additive manufacturing technology to fabricate filter mesh designed with non-stochastic lattice structures. Disc filters with 1-layer, 2-layer and 3-layer thicknesses of repeated 1.8 mm lattice unit cell as the filter mesh are modelled in SolidWorks. Computational Fluid Dynamic (CFD) simulation using ANSYS CFX is performed at eight different flow rates (250-390 L/min) and the results (pressure drop and velocity) are analysed. Simulations are also done for perforated plates with circular-shaped and square-shaped holes with the same aperture size and filter cut point for benchmarking purposes. The outcomes indicate that the pressure drop of the lattice filters is noticeably lower than the perforated plates. These findings show that several layers of lattice structure could be stacked together as filter mesh to increase filtration efficiency with minimal pressure drop and to create a more tortuous path for the fluid.

This paper discusses the operation of a 4 MGD pressurized two stage ultrafiltration (UF) plant over a 14 month period at the Oliver-Mercer-North Dunn (OMND) drinking water treatment facility. The OMND treatment facility utilizes UF followed by low pressure Reverse Osmosis (RO) softening to produce a blended finished water capacity of 3.6 MGD. The 4 MGD capacity of the UF system supplies the feed water for the softening system and a softening bypass system for a blended finished water consisting of 60% softening system product water and 40% UF product water.The plant is located approx. 12 miles (20 km) northwest of Beulah, North Dakota, USA and uses Missouri River water from the Lake Sakakawea reservoir as a source of supply.

The plant experienced a minor issue during start-up in that a shipment issue resulted in all the UF membranes being subjected to sub-zero temperatures (-20ºC) during transportation to site. Unlike flat sheet polyvinylidene fluoride (PVDF) membranes which are shipped dry, pressurized hollow fibre membranes are shipped wet with a preservative solution to ensure the membranes do not dry out. Subjecting the modules to freezing temperatures can result in freezing of the preservative solution as well as drying out of the membrane fibres. Extreme cold, sub-zero, temperatures can cause the fibres to become brittle and allow them to snap easily with any jarring motion. Solutions to these problems include pinning of the broken fibres and re-wetting of the dried fibres with a 40 wt% ethanol solution. For the specific plant at OMND only 2 modules out of 150 were significantly damaged by the low temperature. Both of the damaged modules were pinned and returned to the manufacturer. One of the modules was re-wetted back at the factory. The re-wetted module recovered back to within the manufacturing Quality Control Release Value (QCRV). Five additional modules had damaged fibres but the damaged fibres were limited in number and repaired on-site. The five repaired modules, along with the other modules in the plant appeared to ‘wet-up’ during start up and became tighter, passing less air, resulting in lower pressure decay and higher Log Removal Values (LRVs) over a period of a few days.

To ensure that the integrity of all 150 modules was intact, daily manual logsheet readings along with PLC data was gathered. Data included the start pressure, end pressure and calculated LRV result from the daily Pressure Decay Test (PDT) also known as the Direct Integrity Test (DIT). To ensure a conservative result the LRV calculations used the Darcy pipe flow model. Based on the US EPA Membrane Filtration Guidance Manual1 membrane manufacturers have the option of choosing either the Darcy pipe flow model, which assumes turbulent flow in a breach in the fibre, or the Hagen-Poiseuille model which assumes laminar flow or a combination of the two. The calculated LRV values are always lower using the Darcy pipe flow model. For example, the following was written in an independent challenge test report prepared for the California Department of Public Health for a pressurized UF membrane module similar to the one used at OMND: “The removal efficiency of microspheres was measured at 4.6 and 5.3 log when the Darcy model predicted approx. 4.0 log removal and the Hagen-Poiseuille model predicted approx. 4.7 log removal.” By using the Darcy pipe model a conservative LRV result is assured.

At the OMND plant calculated LRV values are consistently 4.3 log or greater using the Darcy pipe model. Other conservative parameters were also used in the LRV calculations in determining the minimum test pressure required for detection of a 3 µm or smaller breach in the membrane surface. For the pore shape correction factor (K) the most conservative value of 1 was used. For the liquid-membrane contact angle (θ) zero degrees was used as opposed to a measured contact angle. Overall integrity performance of the plant for a 14 month period is discussed in detail. Trans-membrane pressure (TMP), flux, temperature corrected permeability (specific flux) and cleaning efficiency for both the 1st and 2nd UF stages is also presented.

Deliquoring methods have been developed for efficiently reducing the average porosity of filter cake formed by filtration operation without employing any special expression cells. In the methods, filtration was initially conducted using suspension in which particles were flocculated by controlling the solution environment appropriately to produce a high filtration rate. Once the cake formation was complete, the filter cake was further compressed by the principle of reversible flocculation brought about by permeating the solvent in which particles were maintained in a dispersed state.

In this study, the solution environment was controlled in the following three ways:
a) presence or absence of salt in the solvent
b) change of solvent pH
c) presence or absence of alcohol in the solvent.

In these methods the flocculated filter cake formed by a filtration operation in the initial stage, and subsequently the compressed cake with a relatively low moisture content was obtained by solvent permeation through the use of reversible flocculation. The suitability of the methods was determined by performing microfiltration of TiO2 suspensions and subsequent permeation in a deadend mode under the condition of constant pressure.

Volume 16, Issue 1 Abstracts from the FILTRATION journal

E10 FILTRATION: ITS USE IN GAS TURBINE AIR FILTERS AND THE INFLUENCE OF PULSING ON PERFORMANCE
Edward Owen (pages 36-47)

This paper reports the results of a field trial and active test cell challenging of ISO standard EN1822:2009 E10 grade gas turbine (GT) air intake filter cartridges that were designed to assess the effectiveness of pulsing in an urban location. The field trial took place on an operating gas turbine with filters tested and graded as E10 without pulsing. The test cell was a specially constructed mobile miniature filter house with pulsing capability. Statistical data for ambient environmental conditions and pressure drop at both the filter house and the test cell were recorded. The paper aims to show that current E10 technology is the ideal solution for almost all gas turbine installations as it represents the best compromise for perfect filtration. Included in the current work are product justification, trial site data, portable pulse test cell data, independent standard testing, internal product testing and post usage media analysis.

The diesel fuel filter business is a multi-billion dollar industry with hundreds of manufacturers around the world producing a wide variety of products for contamination control in diesel engines and for bulk storage and dispensing applications. Competition to produce these filters and gain a slice of this lucrative market is extremely high and as such, manufacturers are continually striving to gain a competitive edge; be it through product innovation or sales and marketing strategies.

One of the more popular strategies of recent times is to advertise the dirt holding capacity of the filter element, simply represented as total weight in grams or ounces. The current paper is intended to provide an insight into this widely used reference factor and will explore the reasons why the average consumer should avoid using such information as a standalone determining factor for filter selection, or as a predictor of actual filter service life.

Experimental data were obtained using controlled crossflow apparatus for two very different membrane systems. Polymer microfiltration (MF) membranes of differing properties were characterised and used to filter aqueous suspensions carrying colloidal and fine particles of known shape, size, surface charge and chemical composition. By changing the size and size distribution of the feed and the pore size of the membrane in a systematic manner, the influence of the pore/particle size ratio to fouling or cake layer formation is illustrated. By way of contrast the results of some solvent resistant nanofiltration (SRNF) experiments with more hydrophobic membranes and a range of organic solvents and dissolved solutes are also presented. This low fouling system also illustrates the importance of solute size in relation to the size of the transport regions in membranes and presents some interesting correlations with the results obtained for MF.